I think the situation about Trinity and Richland supporting cl_khr_fp64 remains unclear. On Trinity's GPU, the support for cl_khr_fp64 has certainly been there on at least some driver versions that I was aware of.
However, the SDK 2.8 docs state that the Trinity's GPU does not support cl_khr_fp64.
On Richland, the situation is again confusing. Take 8650G, the GPU side of some Richland-based mobile APUs. CLBenchmark site shows the OpenCL environment info here: CLBenchmark - OpenCL Compute Performance of AMD Radeon HD 8650G and cl_khr_fp64 is NOT listed in the available extensions.
Clarity on this issue will be greatly appreciated.